The invention is applicable to bare ladders or to ladders which are caged for protective purposes. A cage ends close to but not at the end of the ladder in order to facilitate access to the ladder.
Regulations exist which require the end hoop of a ladder cage to be provided with a flap which is hinged about a horizontal axis to enable the flap to be locked in the pane of the end hoop, thereby preventing access to the inside of the cage.
However, this technique does not prevent access to the portion of the ladder which extends outside the cage; in addition, once authorized persons have gained access to a cage by opening the flap (e.g. by letting it hang down from its hinge), it is extremely difficult for them to close the flap from inside the cage to prevent unauthorized access to the ladder while they are on it, or after they have left it by its other end.
Preferred embodiments of the present invention avoid the above drawbacks by providing a device for preventing access to a caged ladder in which access is simultaneously prevented both to the end hoop of the cage and to at least a part of the end portion of the ladder situated between its end rung and the end hoop.
Preferred implementations of the invention also provide a device of the above-defined type which can be closed and locked behind persons on the ladder inside the cage, and which can easily be opened, without using a key, when such persons seek to exit from the cage and leave the ladder.
Preferred embodiments of the present invention provide a device of the above-defined type which, in addition, automatically closes and locks behind a person on the ladder inside the cage.
In another aspect, the present invention is also applicable to ladders which are not caged, but which extend from a first level to a second level through a person-passing opening. A person at the first level and seeking to gain access to the second ladder by taking the ladder must pass through the opening.
Such an opening is comparable to the opening defined by the end hoop of a ladder cage. Consequently, in the following description, the term "person-passing opening" is used to designate any opening through which a person taking a ladder must pass in order to go from one level to another. If the ladder is caged, then the person-passing opening is constituted by the end hoop of the cage. If the ladder is uncaged, but passes through a hole in a floor or a deck, then that hole constitutes a person-passing opening.